Feb 12 (Reuters) - A top Montana Department of Livestock official is pushing a proposal to allow hunting of bison inside Yellowstone National Park for the first time in its 142-year-old history to keep their numbers in check.

Marty Zaluski, Montana state veterinarian and member of a federal, state and tribal team that oversees bison in and around Yellowstone, said hunts in the park of the nation's last purebred herd of bison would lessen conflicts tied to their management.

Yellowstone is located primarily in Wyoming but also extends into Idaho and Montana.

"I don't have rose-colored glasses but I see many potential benefits to hunting in the park," he said.

Yellowstone bison, also known as buffalo, are a key attraction for the millions who visit the park each year. But the animals run into trouble in harsh winters when they flee the deep snows of Yellowstone in search of food in lower elevations in Montana.

Cattle ranchers there worry bison might infect their herds with brucellosis, a disease that can cause stillbirths in cows and lower their market value.

Yellowstone managers on Wednesday sent to slaughter 20 bison that wandered into Montana. Park officials had warned earlier this week as many as 800 bison could be shipped to slaughter if they ventured outside the park.

The herd is all that remains of ancient bands that roamed in the tens of millions west of the Mississippi until systematic hunting cut their numbers to the fewer than 50 that found refuge in Yellowstone in the early 20th century.

A management plan overseen by federal, state and tribal representatives that allows killing of wayward buffalo has been fiercely opposed by wildlife advocates and by businesses licensed to provide tours in Yellowstone.

PROTECT CATTLE

Zaluski said hunting of the animals inside the park would protect cattle that graze in Montana near Yellowstone and bring the 4,600-strong herd closer to the population target of 3,000 to 3,500. He said it would also lessen the public relations fallout tied to the slaughter of animals that leave the park.

"What I'm saying here is we have the potential to move this intractable issue forward. Hunting needs to be looked at more seriously as a possible solution," Zaluski said .

Yellowstone spokesman Al Nash said the park was not averse to hunting, a tool long used to manage North American wildlife, but it conflicts with a federal law enacted in 1894 that banned hunting or killing of animals inside the park unless they were threatening injury or death to humans.

The early version of the Lacey Act was crafted in part to address a late 19th century incident in which a man shot several bison dead in Yellowstone, Nash said.

"The status and subject of hunting in Yellowstone ties back to its beginnings and its founding principles," he said.

At the core of the park system's approach is to facilitate nature at work, Nash said.

Hunting and trapping are not allowed in the majority of U.S. parks although legislation that would open the roughly 400 units in the National Park System has been promoted in Congress in recent years.

Steve Braun, owner of Adventure Yellowstone Inc., which offers year-round tours of the park to vacationing Americans and international travelers, said he would fiercely oppose any measure aimed at bison hunts in Yellowstone and criticized the existing management plan that authorizes slaughter.

"Killing these animals is senseless and outrageous. In terms of tourist dollars, they are worth hundreds of millions of dollars a year. In terms of the heritage of the American West, they are priceless," he said.

Nearly one in five of the Yellowstone herd was sent to slaughter for straying into Montana for food in the hard winter of 2006. Under this year's culling program, bison that migrate to winter range in Montana are to be captured and transferred to Native American tribes that would ship them to slaughter. (Editing by Cynthia Johnston and Cynthia Osterman)